1. Field of the Invention
The present invention relates to a dental gypsum-bonded investment material powder which can manufacture a dental metal restoration material having no defect while preventing air bubbles from being mixed into a paste corresponding to a mixed material in the case of being mixed with water.
2. Description of the Conventional Art
The dental metal restoration material is manufactured by procedures of forming a shape of a restoration material by a wax material on the basis of a precise casting technique according to a lost-wax process, attaching a sprue line (a molten metal injection port) thereto, embedding it with a dental embedding material, extracting the sprue line after the dental embedding material is set, and injecting a molten metal into a cavity which is formed by burning and removing the wax. Particularly, the dental metal restoration material is demanded a higher dimensional precision since the dental metal restoration material is installed to an oral cavity so as to be used for the purpose of restoring a defect part of the tooth. In order to obtain the dental metal restoration material which is excellent in precision, it is necessary to compensate a casting shrinkage of the metal, by utilizing an expansion of the dental embedding material when the dental embedding material is set and heated.
The dental embedding material generally has two kinds of material including a gypsum-bonded investment material obtained by mixing a fire resisting material such as quartz and/or cristobalite with an α hemihydrate gypsum as a bonding material, and a phosphate-bonded investment material obtained by mixing the fire resisting material such as the quarts and/or the cristobalite with an ammonium dihydrogenphosphate and a magnesium oxide as a bonding material, and having a high heat resistance. In the case of a dental casting alloy of noble metal for inlaying, crowning and bridging which is defined by JIS standard as a liquid phase point is equal to or lower than 1000 to 1100° C. [dental casting silver alloy (JIS T 6108), dental casting gold, silver and palladium alloy (JIS T 6106), dental casting gold alloy (JIS T 6116)], the gypsum-bonded investment material is used, and in the case of a dental casting porcelain baking noble metal alloy which has a high liquid phase point (equal to or higher than 1100° C.) so that the alloy can stand against a baking work (about 1000° C.) of the porcelain after casting, the phosphate-bonded investment material is used.
An importance for the precise dental restoration material exists in a matter that the air bubbles are not mixed into the paste corresponding to the mixed material at a time when the dental gypsum-bonded investment material powder and the water are mixed. In the dental gypsum-bonded investment material, since the air is included generally in the investment material powder, the air bubbles tend to enter into the dental gypsum-. If the air bubbles are mixed into the paste, a concave shape is formed by casting into the dental metal restoration material. Therefore, a repairing operation such as a trimming operation is necessary after the casting.
In order to reduce the air bubbles which are generated at the mixing time, there is a defoaming method of a dental material mixed material which agitates the mixed material by using a defoaming device in which a handle portion is attached to a defoaming member having a curved surface (refer, for example, to patent document 1). However, this method needs employment of a dedicated device.
Consequently, there has been developed a dental gypsum-bonded investment material powder which generates less air bubbles at a time of being mixed. For example, there is a mixing method of adding an emulsion structured such that an anionic surfactant is dispersed as an emulsifying agent into the water to a silicone oil, which is carried out in a dental gypsum field (refer, for example, to patent documents 2 and 3). However, in these methods, it is necessary to prepare the dedicated emulsifying agent in addition to the powder and the water, a handling has been complicated. Further, there has been a defect that it is necessary to prepare the dedicated mixing solution even if the emulsifying agent is mixed with the water. Further, since the anionic surfactant is mainly used for a mold release agent in relation to the wax, there has been a problem that the powder is hydrophobic and it is hard to mix with the water.    Patent Document 1: Japanese Unexamined Patent Publication No. 5-155731    Patent Document 2: Japanese Unexamined Patent Publication No. 6-133990    Patent Document 3: Japanese Unexamined Patent Publication No. 6-178926